Stability of the longitudinal mode in λ/4-shiftedInGaAsP/InP DFB lasers

Factors causing the mode stability of λ/4-shifted distributed-feedback (DFB) lasers, spatial hole burning along the laser axis and residual reflectivity of the facets of laser cavity, are studied. It is experimentally and theoretically confirmed that the spatial hole burning increases the corrugation phase shift from λ/4 (π) to 3λ/8 (1.5 π) as the driving current increases in lasers whose coupling constant and cavity-length product kL is 2.0. This hole-burning effect requires the reflectivity of facets to be reduced below 0.2% to get a high reproducibility of lasers oscillating at a stable single mode up to high output powers     

Theoretical analysis of tuning properties for a phase-tunable DFBlaser

The device consists of a conventional or a λ/4-shifted DFB (distributed-feedback) laser monolithically integrated with an external waveguide section with separate electrodes for phase control. Tuning curves are presented for threshold current, frequency, linewidth, and output power. The analysis demonstrates a generally higher side mode suppression and larger frequency tuning range but also a larger linewidth for the λ/4-shifted device compared to the device with a conventional DFB section     

Complex-coupled λ/4-shifted DFB lasers with a flat FMresponse from 10 kHz to 17 GHz

Semiconductor lasers with a flat FM response are required for coherent FSK transmission systems. A complex-coupled λ/4-shifted DFB laser is described that gives a flat FM response from 10 kHz to I7 GHz at 15 mW, achieved by using the self-suppressing mechanism of the spatial hole-burning effect     

Spectral linewidth of DFB lasers including the effects of spatialholeburning and nonuniform current injection

An analytic expression for the linewidth of distributed-feedback (DFB) lasers is derived. Local fluctuations in carrier density are shown to provide a significant contribution to laser linewidth in the presence of spatial holeburning. In a single-electrode DFB laser the effect can be avoided by careful optimization of the kl-product, but for a multielectrode DFB laser the linewidth can also be reduced by adjusting the injected current profile to compensate for spatial holeburning. Numerical results for a three-electrode λ/4-shifted DFB laser are presented     

Analysis of surface-emitting λ/4-shifted DFB lasers with adistributed Bragg reflector

Threshold current density and differential quantum efficiency are analyzed for a surface emitting (SE) λ/4-shifted distributed feedback (DFB) laser consisting of alternating active and passive layers with a distributed Bragg reflector (DBR). It is shown that the threshold current density can be reduced by using the DFB action induced by alternating active and passive layers in the active region of the SE DFB laser structure, as compared to SE DBR lasers with a homogeneous active region. It is also shown that the differential quantum efficiency of the DFB laser with a DBR can be higher than that of conventional DBR lasers without increasing the threshold current density     

Spontaneous emission model of surface-emitting DFB semiconductorlasers

A general spontaneous emission model is developed for surface-emitting (SE) distributed feedback (DFB) semiconductor lasers. The frequency distribution of spontaneous emission noise below lasing threshold and the spontaneous emission rate in lasing operation are formulated by using a transfer matrix method combined with the Green's function method. The effective linewidth enhancement factor is obtained from this model in terms of the elements of the transfer matrix. By way of example, the author applies the formulation to a standard SE DFB laser, and a SE λ/4-shifted DFB laser with a distributed Bragg reflector (DBR) mirror. In particular, the author analyzes the below-threshold spectrum, the threshold current density, the differential quantum efficiency, and the spectral linewidth of these lasers     

FM response of narrow-linewidth, multielectrode λ/4 shiftDFB laser

Flat FM response from 100 kHz to 15 GHz was achieved in a multielectrode distributed-feedback (DFB) laser. A λ/4-shifted corrugation and a 1200-μm-long cavity were very effective not only in reducing the linewidth to less than 1 MHz, but also in making FM response flat by selective current injection     

Nondegenerate four-wave mixing in a long-cavity λ/4-shiftedDFB laser using its lasing beam as pump beams

In this paper, we discuss nondegenerate four-wave mixing in a lasing long-cavity λ/4-shifted DFB laser using the laser beams as pump beams. A high conversion efficiency and wide conversion range were experimentally demonstrated without the assistance of Fabry-Perot resonance. Electric field profiles of the pump, signal, and conjugate beam in our λ/4-shifted DFB laser are discussed. The third-order nonlinear susceptibilities of InP-InGaAs MQW's are then estimated from the experimental results. We discuss the saturation characteristics and the ratio of the conjugate power to the amplified spontaneous emission. We show that λ/4-shifted DFB lasers are suitable for wavelength converters using nondegenerate four-wave mixing because of their ability to provide single-device operation     

External feedback sensitivity of partly gain-coupled DFBsemiconductor lasers

External optical feedback sensitivity of partly gain-coupled DFB semiconductor lasers has been analyzed in above threshold operation regime. Both the longitudinal spatial hole burning and the nonlinear gain compression have been taken into account. A comparison has been made among λ/4-shifted, pure index-coupled and partly gain-coupled DFB laser diodes. Even though pure index-coupled and partly gain coupled DFB lasers exhibit similar sensitivity to external optical feedback at the threshold, however, gain grating can reduce the feedback sensitivity when the lasers operate well above the threshold specially when the κL parameter is high     

Transient chirping in distributed-feedback (DFB) lasers: effect ofspatial hole-burning along the laser axis

An analysis of the chirping behavior of directly modulated distributed-feedback (DFB) lasers which takes into consideration the effects of spatial hole-burning along the laser axis is discussed. Rate equations including these effects are derived. To calculate the rate equations, the threshold condition of phase-shifted DFB lasers with a nonuniform refractive index distribution is analyzed. The calculations are carried out on phase-shifted DFB structures under the condition of random nonreturn to zero modulation at 1.8 Gb/s. The results show that the spatial hole-burning along the axis significantly affects the chirping behavior, adding to the effects induced by the spectral hole-burning alone     

Suppression of external cavity modes in DFB lasers with a highendurance against optical feedback

This paper clarifies that the external cavity modes deform optical output response in the DFB lasers by enhancing the relaxation oscillation under NRZ modulation. It is shown that a DFB laser with an asymmetric structure in reflectivity of facets and in position of a λ/4 phase shift can suppress the influence of the external cavity modes     

Gain-coupled DFB lasers versus index-coupled and phase shifted DFBlasers: a comparison based on spatial hole burning corrected yield

A statistical yield analysis is presented for gain- and index-coupled distributed feedback (DFB) laser structures, allowing a comparison of their single longitudinal mode (SLM) yield capabilities. For the yield calculations, the threshold gain difference and the longitudinal spatial hole burning (SHB) are taken into account. By comparing the experimental and theoretical yield of index-coupled DFB lasers, the significance of SHB for correct yield predictions is illustrated. For the purpose of comparison, yield calculations for various λ/4-shifted DFB lasers (with low facet reflectivities) are presented. The most emphasis, however, is on partly gain-coupled DFB lasers. Estimations of practical gain coupling coefficient values for gain and for loss gratings are discussed     

Effect of linear gain saturation on small-signal dynamics of MQWDFB lasers

The linear gain saturation effect is shown to be important in determining the dynamics of multiple-quantum-well (MQW) distributed-feedback (DFB) lasers. A more realistic logarithmic dependence of material gain on carrier density is assumed in a comprehensive MQW DFB laser model. It is found through simulation that because of the linear gain saturation, the interplay between modal gain and differential gain leads to an optimal κL for maximum small-signal modulation bandwidth in λ/4-shifted MQW DFB lasers     

The design assessment of λ/4 phase-shifted DFB laserstructures

A detailed nonlinear model of the performance of single-frequency laser structures operating both below and above threshold is discussed. Arbitrary series combinations of uniform pitch grating, linearly-chirped pitch grating and plane guide sections can be analyzed-taking longitudinal-mode spatial hole burning into account. The material properties of each section of a device structure can be specified. The output power from each end of the laser and the emission wavelength, and the longitudinal intensity, carrier density, and relative permittivity profiles are predicted as a function of drive current above threshold for each lasing mode. The linewidth is also estimated while allowing for the nonuniform longitudinal distribution of spontaneous emission into the mode in a physical manner. The model was used to provide the data with which to trade off the numerous interacting performance parameters of a λ/4 phase-shifted DFB (distributed-feedback) laser. The design options are then summarized     

Effect of axial hole-burning on TM mode suppression in λ/4phase-shift DFB lasers

The TM mode suppressibility in λ/4 phase-shift distributed feedback (DFB) lasers is analysed by considering the effect of the axial hole-burning. The calculated result shows that the hole-burning always decreases the threshold gain difference between the TE and TM modes     

掺Yb相移分布反馈光纤激光器的后期制作与研究

采用二次曝光法先在一根10cm长的掺Yb光纤上制作出近似λ/4相移分布反馈(DFB)掺Yb光纤激光器。再利用紫外修整的方法,同时通过F-P扫描干涉仪及示波器实时监控激光运行模式,获得了阈值低而单纵模运行特性好的λ/4相移DFB掺Yb光纤激光器。所制作的激光器阈值为20mW。当抽运功率为130mW时,获得了25mW的1053um单纵模激光。     

Two-dimensional numerical simulator for multielectrode distributedfeedback laser diodes

A two-dimensional program for the analysis of multielectrode distributed feedback (DFB) laser diodes under nonuniform carrier injection conditions has been developed. The program self-consistently solves the carrier transport together with optical equations. In addition, the present simulation system offers a user-friendly graphic interface during input and output stages. The effectiveness of the program has been demonstrated through a three-section DFB LD. The improvement of the spatial hole burning effect under nonuniform carrier injection has been elucidated by directly monitoring the carrier and/or current density distribution and indirectly evaluating the cavity loss     

Analysis of wavelength conversion using highly nondegeneratefour-wave mixing in λ/4-shifted DFB lasers

We present a theoretical analysis of terahertz-range wavelength conversion using highly nondegenerate four-wave mixing in λ=1.55 μm, medium-coupling λ/4-shifted distributed feedback (DFB) lasers. Based on the coupled-wave approach, our model predicts up to ~2 THz probe-pump detuning with a -20 dB or higher conversion efficiency for quantum-well λ/4-shifted DFB. The influences of pump power and DFB coupling strength (κL) on wave mixing as well as the Bragg reflection effects are discussed. The predictions of the model are found to be in good agreement with recent experimental observations     

Narrow-linewidth 1.3 μm DFB-DCPBH lasers with λ/4-shiftedfirst-order gratings fabricated by electron beam lithography using a newfast resist

GaInAsP-InP 1.3 μm DFB-DCPBH lasers were made with λ/4-shifted first-order gratings fabricated by electron beam lithography using a new fast resist, poly(3-butenyl-trimethylsilane sulfone). The devices had a threshold current of 17 mA, a submode suppression ratio of 39 dB, and a minimum linewidth of 4.4 MHz at 15 mW. By heterodyning two DFB lasers, the authors obtained a beat frequency of 1.5 GHz with 12 MHz FWHM     

Ultralow chirp and high-speed 1.55 μm multiquantum wellλ/4-shifted DFB lasers

An ultra-low-chirp, high-speed, 1.55-μm, multi-quantum-well (MQW), λ/4-shifted, InGaAsP distributed-feedback (DFB) laser is demonstrated. A record chirp width of 0.4-0.5 nm (20-dB down full width) is achieved at 10-Gb/s direct modulation. This low-chirp single-longitudinal-mode operation is attained by an increase in the quantum size effect in the MQW active layer